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The smut Ustilago maydis, a ubiquitous pest of corn, is highly adapted to its host to parasitize on its organic carbon sources. We have identified a hexose transporter, Hxt1, as important for fungal development during both the saprophytic and the pathogenic stage of the fungus. Hxt1 was characterized as a high-affinity transporter for glucose, fructose, and mannose; ∆hxt1 strains show significantly reduced growth on these substrates, setting Hxt1 as the main hexose transporter during saprophytic growth. After plant infection, ∆hxt1 strains show decreased symptom development. However, expression of a Hxt1 protein with a mutation leading to constitutively active signaling in the yeast glucose sensors Snf3p and Rgt2p results in completely apathogenic strains. Fungal development is stalled immediately after plant penetration, implying a dual function of Hxt1 as transporter and sensor. As glucose sensors are only known for yeasts, ‘transceptor’ as Hxt1 may constitute a general mechanism for sensing of glucose in fungi. In U. maydis, Hxt1 links a nutrient-dependent environmental signal to the developmental program during pathogenic development.

Background Colletotrichum graminicola is a hemibiotrophic fungal pathogen that causes maize anthracnose disease. It progresses through three recognizable phases of pathogenic development in planta : melanized appressoria on the host surface prior to penetration; biotrophy, characterized by intracellular colonization of living host cells; and necrotrophy, characterized by host cell death and symptom development. A “Mixed Effects” Generalized Linear Model (GLM) was developed and applied to an existing Illumina transcriptome dataset, substantially increasing the statistical power of the analysis of C. graminicola gene expression during infection and colonization. Additionally, the in planta transcriptome of the wild-type was compared with that of a mutant strain impaired in the establishment of biotrophy, allowing detailed dissection of events occurring specifically during penetration, and during early versus late biotrophy. Results More than 2000 fungal genes were differentially transcribed during appressorial maturation, penetration, and colonization. Secreted proteins, secondary metabolism genes, and membrane receptors were over-represented among the differentially expressed genes, suggesting that the fungus engages in an intimate and dynamic conversation with the host, beginning prior to penetration. This communication process probably involves reception of plant signals triggering subsequent developmental progress in the fungus, as well as production of signals that induce responses in the host. Later phases of biotrophy were more similar to necrotrophy, with increased production of secreted proteases, inducers of plant cell death, hydrolases, and membrane bound transporters for the uptake and egress of potential toxins, signals, and nutrients. Conclusions This approach revealed, in unprecedented detail, fungal genes specifically expressed during critical phases of host penetration and biotrophic establishment. Many encoded secreted proteins, secondary metabolism enzymes, and receptors that may play roles in host-pathogen communication necessary to promote susceptibility, and thus may provide targets for chemical or biological controls to manage this important disease. The differentially expressed genes could be used as ‘landmarks’ to more accurately identify developmental progress in compatible versus incompatible interactions involving genetic variants of both host and pathogen.

Background Sugarcane smut can cause losses in cane yield and sugar content that range from 30% to total crop failure. Losses tend to increase with the passage of years. Sporisorium scitamineum is the fungus that causes sugarcane smut. This fungus has the potential to infect all sugarcane species unless a species is resistant to biotrophic fungal pathogens. However, it remains unclear how the fungus breaks through the cell walls of sugarcane and causes the formation of black or gray whip-like structures on the sugarcane plants. Results Here, we report the first high-quality genome sequence of S. scitamineum assembled de novo with a contig N 50 of 41 kb, a scaffold N 50 of 884 kb and genome size 19.8 Mb, containing an estimated 6,636 genes. This phytopathogen can utilize a wide range of carbon and nitrogen sources. A reduced set of genes encoding plant cell wall hydrolytic enzymes leads to its biotrophic lifestyle, in which damage to the host should be minimized. As a bipolar mating fungus, a and b loci are linked and the mating-type locus segregates as a single locus. The S. scitamineum genome has only 6 G protein-coupled receptors (GPCRs) grouped into five classes, which are responsible for transducing extracellular signals into intracellular responses, however, the genome is without any PTH11-like GPCR. There are 192 virulence associated genes in the genome of S. scitamineum , among which 31 expressed in all the stages, which mainly encode for energy metabolism and redox of short-chain compound related enzymes. Sixty-eight candidates for secreted effector proteins (CSEPs) were found in the genome of S. scitamineum , and 32 of them expressed in the different stages of sugarcane infection, which are probably involved in infection and/or triggering defense responses. There are two non-ribosomal peptide synthetase (NRPS) gene clusters that are involved in the generation of ferrichrome and ferrichrome A, while the terpenes gene cluster is composed of three unknown function genes and seven biosynthesis related genes. Conclusions As a destructive pathogen to sugar industry, the S. scitamineum genome will facilitate future research on the genomic basis and the pathogenic mechanisms of sugarcane smut.

Climate change forces agriculture to face the rapidly growing virulence of biotrophic fungal pathogens, which in turn drives researchers to seek new ways of combatting or limiting the spread of diseases caused by the same. While the use of agrochemicals may be the most efficient strategy in this context, it is important to ensure that such chemicals are safe for the natural environment. Heterocyclic compounds have enormous biological potential. A series of heterocyclic scaffolds (1,3,4-thiadiazole, 1,3-thiazole, 1,2,4-triazole, benzothiazine, benzothiadiazine, and quinazoline) containing 2,4-dihydroxylaryl substituents were investigated for their ability to inhibit the growth and development of biotrophic fungal pathogens associated with several important cereal diseases. Of the 33 analysed compounds, 3 were identified as having high inhibitory potential against Blumeria and Puccinia fungi. The conducted research indicated that the analysed compounds can be used to reduce the incidence of fungal diseases in cereals; however, further thorough research is required to investigate their effects on plant–pathogen systems, including molecular studies to determine the exact mechanism of their activity.

• Conversion of surface-exposed chitin to chitosan in cell walls of in vitro- and in vivo-differentiated infection structures of two rust fungi, the wheat stem rust fungus Puccinia graminis f. sp. tritici and the broad bean rust fungus Uromyces fabae, and of the causal agent of maize anthracnose, Colletotrichum graminicola, were studied. • Epi-fluorescence microscopy with the fluorescence-labeled lectin wheat germ agglutinin (WGA) revealed that surfaces of infection structures formed on the plant cuticle expose chitin, whereas surfaces of structures formed after invading the host do not. • To identify chitin modification by de-N-acetylation, we raised polyclonal antibodies specifically recognizing de-N-acetylated chitosan. These antibodies labeled only those infection structures that differentiate inside the plant, indicating that chitosan is exposed on cell wall surfaces post penetration. • Surface modification of the fungal cell walls by chitin de-N-acetylation is discussed as a fungal strategy to protect cell walls of pathogenic hyphae from enzymatic hydrolysis by host chitinases, and to avoid generation of an auto-catalytic defense response system in the invaded host tissue.

Pneumocystis species are obligate fungal biotrophs that colonize the lungs of mammals. They cause deadly pneumonia in immunocompromised hosts. Pneumocystis species are obligate fungal biotrophs that colonize the lungs of mammals. They cause deadly pneumonia in immunocompromised hosts. The sexual phase seems obligate during their life cycle and essential for survival because it is believed to ensure proliferation and transmission between hosts. Here, we consider if the sexual phase is initiated by the fusion of two cells or by nucleus duplication in order to generate diploid cells that can undergo meiosis. The juxtaposition of the nucleus-associated organelles of pairs of cells with fused cytoplasmic membranes demonstrated that cell fusion can occur. Nevertheless, the frequency of cell fusion remains to be determined, and it cannot be excluded that both cell fusion and nucleus duplication are used to ensure the occurrence of the essential sexual phase. In vitro culturing of these fungi is a major milestone that could clarify the issue.

Over the past few decades, peanut smut, caused by Thecaphora frezzii, has evolved from an emerging disease to a major global threat to peanut production. However, critical knowledge gaps persist regarding the anatomical pathways and host responses involved in infection, colonization, and sporulation. This study examines the pathosystem and histopathology of the biotrophic phase of T. frezzii in the susceptible cv. Granoleico. Anatomical analyses were conducted using light microscopy, confocal laser scanning, and scanning electron microscopy. Our findings reveal that T. frezzii enters the host through the peg rather than the ovary tip, invading during the R2-subterranean phase. Fruit colonization occurs at the R3-stage when the mechanical layer between the mesocarp and endocarp has not yet formed. Hyphal entry into the seed takes place between the R3-medium and R3-late pod stages via the funiculus, leading to extensive seed coat colonization without penetrating the embryo. Once inside, hyperplasia and hypertrophy are triggered, coinciding with teliospore formation. Teliosporogenesis disrupts nutrient translocation, arresting embryo development. The hyphae colonize tissues intracellularly, utilizing living cells of the vascular bundles and following the peanut’s photoassimilate transport pathway. Investigating these structural responses in phenotypically contrasting peanut genotypes may provide key insights into the anatomical barriers and defense mechanisms that determine disease susceptibility and resistance, ultimately contributing to the development of resistant cultivars.

Miridae is the largest Heteroptera family, with a tremendous worldwide economic impact, both as pests and natural enemies. Unlike most Hemiptera, herbivorous and omnivorous mirid bugs are lacerate/macerate and flush feeders, not phloem feeders. Plant responses to damage by arthropods of this feeding guild therefore occur via jasmonic acid or ethylene signaling pathways rather than the salicylic acid pathway. Moreover, unlike most other Heteroptera that lay eggs on the plant surface, mirids insert their eggs in plant tissues, resulting in oviposition injury. Similarly, regarding phytopathogenic fungi and oomycetes, a distinction should be made between biotrophic fungi (triggering the salicylic acid pathway plant response), and necrotrophic and/or hemibiotrophic fungi or oomycetes (triggering jasmonic acid or ethylene pathway plant responses). In that respect, phytopathogenic fungi or oomycetes (PFO) differ from phytopathogenic viruses and bacteria, the former being all biotrophic while the latter are theoretically hemibiotrophic. Here, for the first time, we review tripartite interactions between mirids, PFO, and crop plants. The major deliverables are as follows: Five major interaction frameworks are identified: (i) crop plant infection by PFO mechanically facilitated by prior mirid infestation; (ii) crop plant infection by PFO hampered by prior mirid infestation via crop plant signaling; (iii) crop plant infestation by mirids facilitated by prior PFO infection via crop plant signaling; (iv) crop plant infestation by mirids hampered by prior PFO infection via crop plant signaling; (v) crop plant infestation by mirids and/or infection by PFO hampered by prior mirid infestation and/or PFO infection via crop plant resource quality alteration. PFO and mirids may also occur concomitantly, favored by the same conditions, i.e., climatic or linked to endogeneous factors (e.g., redox status) in crop plant. Instances from each framework are described, and highlighted interactions are examined in view of managing mirid–PFO complexes on crop plants.

Tritirachium egenum sp. nov., a biotrophic mycosymbiont, was found growing in association with a Penicillium rugulosum. This new species was unable to grow in axenic culture on traditional semi-synthetic culture media unless the growth medium was supplemented with a fraction of the culture filtrate of its host. The hot water extract of Alternaria alternata, containing the 'growth factor' of several contact mycosymbionts (biotrophic contact mycoparasites) also supported the growth of T. egenum. Signs, particularly the functional equivalence of this extract and ferrichrome on the T. egenum growth, suggested that this growth factor, referred to in the literature as mycotrophein, could actually be a hydroxamate-type siderophore. Moreover, it was shown that this siderophore-dependent organism had a deficient metabolism requiring, in addition, an exogenous source of thiamine or a precursor molecule of thiamine. Among mycosymbionts of fungi, the nutrient acquisition strategy of T. egenum is new, because it did not live in close association with the cytoplasm of its host. Indeed, it is neither a haustorial mycosymbiont nor a contact mycosymbiont, the two groups into which the biotrophic mycosymbionts of fungi are classified. Moreover, an interfungal association based on the utilization of siderophores has not yet been reported.

Witches' broom disease (WBD) is caused by the hemibiotrophic basidiomycete fungus Crinipellis perniciosa, which is one of the most important diseases of cocoa in the western hemisphere. In this study, the contents of soluble sugars, amino acids, alkaloids, ethylene, phenolics, tannins, flavonoids, pigments, malondialdehyde (MDA), glycerol, and fatty acids were analysed in cocoa (Theobroma cacao) shoots during the infection and development of WBD. Alterations were observed in the content of soluble sugars (sucrose, glucose, and fructose), asparagine and alkaloids (caffeine and theobromine), ethylene, and tannins. Ethylene and tannins increased prior to symptom development and declined with the death of the infected tissues. Furthermore, MDA and glycerol concentrations were higher in infected tissue than in the controls, while fatty acid composition changed in the infected tissues. Chlorophylls a and b were lower throughout the development of the disease while carotenoids and xanthophylls dropped in the infected tissue by the time of symptom development. These results show co-ordinated biochemical alterations in the infected tissues, indicating major stress responses with the production of ethylene. Ethylene levels are hypothesized to play a key role in broom development. Some of the other biochemical alterations are directly associated with ethylene synthesis and may be important for the modification of its effect on the infected tissues.